Aircraft temperature control



H. T. SPARROW AIRCRAFT TEMPERATURE CONTROL Original Filed Nov. 30, 1942 April 25, 195o 2 Sheets-Sheet 1 2 Sheets-Sheet 2 H NSN um H. T. sPARROw AIRCRAFT TEMPERATURE oNTRoL April 25, 195o Original Filed Nov. 50, 1942 QNNJ, RM

APatented Apr. 25, 1950 Hubert 'l'. Sparrow, Minneapolis, Minn., assignor to Minneapolis-Honeywell y Regulator Company, Minneapolis, Delaware nn., a. corporation of original application November so, 1942, serial No. 467,385. Divided and this application February 20, 1946, Serial No. 648,943

`'Ifhe present invention is particularly directed tothe'control ofk temperature in aircraft but it is to'be that certain 'features of the system offcontrolhave a broad general utility wherever it is to variably position two or more devices inseuuence from a single controlling devicewh'ereineach of the devices to be positioned orffans, commonlyknown as compressors, which4 compresstheair from the outside atmosphere and deliver itto theiaircraft cabin so as to maintain a higher pressure therein. Such compressors are'often driven vdirectly from the aircraft engine and their'effect may be controlled, for example, bythe use of a valve or damper which controls the supply ofoutside air to the compressor or discharged by the compressor. Such valves `or dampers may be controlled in any desired manner and at the present time are often controlled manually. Furthermore, the reduc- 13 Claims. (Cl. 257-3) tionfinvpressurewhen ying at altitudes up to eight thousandfeet,` for example, does not cause anyparticular dilliculty with the result that the compressors,A yaltlioughf'they may operate constantly whenever `the aircraft engines are runningpare'not'futilizedftoy do any effective work until anfaltitude of approximately eight thousand'feetis reached.` -v In' other words. instead of trying toniaintainra pressure within the cabinequal to 'thestandard' pressure at sea level, the pressure` withintth'ercabin may be maintained equal Lto thestandard pressure at eight'thousand feet. ".vThe"compression 'ofthe air by the compressors causes-fsuch'fair :toxbe heated and the present invention contemplates utilizing as much or `as littlefof thefheatsof the air heated by 'compression as may benecessaryl for maintaining desii-,edu temperatures 1 fwithinn4 `the aircraft cabin. To fthisendfone :orxmoreafter coolers may be utilizedffoncooling the hot compressed air by thercoolenoutside-air to `any extent desired.

It is an object of the present invention to maintain desired temperatures within an aircraft cabin by utilizing the hot compressed air used for variable character.

pressurizing the cabin and controlling the temperature of such hot compressed air so as to obtaitrx the desired temperature within the aircraft ca m.

At the lower altitudes where very little if any compressing of the air takes place, since this may not be necessary in order to maintain the desired pressure within the cabin, there is often insufficient heat developed by the compressors to maintain the aircraft cabin-at the desired .temperature.

It is therefore an 'object of the present invention additionally to utilize auxiliary heaters to maintain desired temperature conditions Within the aircraft cabin but to use such auxiliary heaters only when the compressors for pressurizing the ca-bin do not deliver sumcient air at a high enough temperature to maintain the desired temperature conditions within the aircraft cabin.

It will be obvious that the output of an auxiliary heater, such as a gasoline red heater, can be predetermined by the design and size of the heater. At the same time, the amount of heat furnished by the compressors is of an extremely It depends, among other things, upon the temperature of the outside air being compressed as well as by the amount of compression taking place. In other words, the maximum output of the compressors in the form of heated air, as distinguished from the quantity thereof, may well vary for any given altitude due to variations in the temperature of the outdoor air, even though a constant pressure is being maintained within the cabin. l'

A further object of the invention, therefore, is

-to control the temperature of the air being delivered by the comprsors to an auxiliary heater at a predetermined value or within a predetermined range of temperatures during such times as it is necessary to utilize the heating eiect of the auxiliary heater.

In addition, many types of auxiliary heaters, while being capable of having their output or capacity modulated or varied over a rather wide range, can only have their capacityv reduced to a certain percentage and then must be turned on entirely. .For example, one well known type of gasoline heater may have its output modulated down to 15 per cent oi its full capacity without any diiliculty -by reducing the supply of fuel thereto but may not safely be modulated below fteen per cent. This means that when such a heater is initially turned on, it must start up at a minimum of fifteen per cent of its' full capacity. However, at such time. the demands may be such as to only exceed the capacity of the compressors by say live per cent of the auxiliary heater capacity." Some heat is clearly needed over and above that furnished by the compressors but the fifteen per cent minimum capacity of the auxiliary heater is too much heat.

It is therefore a further object of the present invention to reduce the heat output of the compressors when the auxiliary heater is rst turned on, in order to compensate for the large increase inglmat which would otherwise occur upon the initial turning on of the auxiliary heater.

From the foregoing it will be seen that the present invention contemplates modulating a rst device (the means for controlling the temperature changing effect of the compressor) and then thereafter modulating a second device (the auxiliary heater) in sequence. Theoretically, this of course could be accomplished in any number of manners but from a practical standpoint these devices must be power driven and are often at points remote from each other. The present invention therefore contemplates providing each of the devices with its own separate power driving means and arranging the control system in such manner that the separate power driving means are controlled in a desired sequence so that the one device moves throughout a considerable range of movement while the second device remains stationary, the second device then moving throughout its range of movement upon further demands.

It is therefore a further object of the present invention to automatically control a pair of power operated devices from a single controller so that they are modulated in sequence, that is, they are not modulated together over their entire range of movement.

Additionally, it is an object of the present invention to modulate a pair of devices in sequence wherein the second device must initially be moved through a substantial part of its movement and substantially simultaneously retracting part of the movement of the first device in order to compensate for this substantial initial movement of the second device.

The power means for the devices preferably takes the form which remains stationary normally and requires the application of power to move the devices in either direction.

Another object of the invention then is the modulation of two such power devices in sequence.

Another object of the invention is the provision of a follow-up type of system in which two or more devices each are capable of producing a predetermined portion of the complete followup action, which portions are less than the complete follow-up action, so that upon wide changes in demand, each device is actuated throughout a range of movement corresponding to its por.- tion of the complete follow-up action. Thus, the two devices move independently of each other. V

The power devices are preferably electrical and are preferably controlled from a single balanced bridge circuit. Each device is capable of producing a certain rebalancing action which is only a portion of the complete rebalancing action, the rebalancing actions of the two or more devices 'taken together being suicient to rebal.- ance the bridge regardless of the amount of unhalance. However, neither device above is capable'of providing the entire rebalancing action.

Other objects of the invention reside in specic details of the present system, various features of adjustment, and other features of the system as a whole and will become apparent upon a reading of the following detailed description in connection with the accompanying drawings, in which:

Fig. 1 is a diagrammatic showing of a portion of an aircraft fuselage showing the general arrangement and interconnection of the temperature control system. and

Fig. 2 is a detailed circuit showing the manner in which the apparatus of Fig. 1 is controlled.

This application is a division of Patent 2,408,- 699, issued October 1. 1946.

Referring first to Fig. 1, the fuselage oi' an aircraft is partially indicated in dotted lines at I0. The fuselage is provided with a forward sealed cabin Il and a rear or ait cabin I2 which is likewise sealed. Air is supplied to the forward cabin II and aft cabin I2 under pressure, for maintaining a desired pressure in such cabins, by a pair of compressors I3 and I4. The compressor I3 is located on the right-hand side of the aircraft and is supplied with air from the outside atmosphere, as by an intake I5. This air is delivered by a duct I5 to a heat exchanger or after 25 cooler I1 in which the air, which is heated by compression, may be cooled by passing outside air thereover through the after cooler as indicated by the arrows at the top of the after cooler I1. The ow of outside air through the righthand after cooler Il is controlled by shutters or damper means, herein conveniently illustrated as a single damper I4, although of course in actual practice such damper means might well be broken up into a number of smaller components. The air then passes by way of a duct I! through a swing check valve and then through ducts 2l, 22 and 23 to the intake or inlet side of an auxiliary heater 24. The air then passes by a duct 25 to the forward cabin II into which it is discharged through an outlet 25.

The left-hand compressor I4 similarly takes in outside air through an intake 21 and the compressed air passes to a left-hand after cooler 28 by way oi' a duct 29. The left-hand after cooler 28 is also cooled by the flow of outside air therethrough as indicated by the arrows and such flow of outside air is herein shown as controlled by the single damper or shutter 30. The compressed air then goes by way of a duct 3|, through a check valve 32, and a duct 25 which joins the ducts 2l and 22.

Some of this air is also supplied to the aft cabin I2. For this purpose, a duct 34 connects between ducts 22 and 23 and leads to the inlet or intake of an auxiliary heater 35. The air then passes through the heater 35 to the aft cabin I2 by way of a duct 35 and outlet 31.

The damper I8 of the right-hand after cooler I1 is varyingly or modulatingly positioned, in a manner which will be hereinafter described in detail, by an electrical modulating motor 38. This motor is provided with a crank arm 39 which is connected to a second crank arm 40 by a link 5 I. The crank arm 40 is 'in turn connected to the damper I8. In addition, the modulating motor 2l is internally provided with a balancing contact finger 52, the purpose of which will be explained in detail hereinafter. In a similar manner, the damper 30 of the left-hand after cooler 28 is positioned by an electrical modulating motor 53 having a crank arm 54 and an internal balancing contact finger 45. The crank arm 54 is connected to a crank arm 48, that is connected to the damper 3l, by a link 41. The auxiliary heater 24 may be of any desired type and may well take the form of the well known Stewart-Warner gasoline heater. Fuel is fed to the heater 24 by a fuel supply pipe 56 which has located therein a modulating fuel supply valve 51 and an on and oif solenoid type fuel supply valve 9. The modulating valve 51 includes an electrical modulating motor mechanism 58 that is provided with a crank arm 59. The crank arm 59 is connected to an operating crank 60 of the valve 51 by a link 6|.

` Inaddition, the motor mechanism 58 is provided with an internal balancing contact finger 62 to which is connected a switch operating member 63, of insulating matetact 1I and further moves a switcharm 12 away from a vcontact `13 `and into engagement with a contact Y14. Engagement of switch arm with contact 1| `energires the solenoid valve 9- and supplies power to the terminal panel of the heater 24 as follows: line wire 15, switch arm 10,

contact 1| and wire' 16 where the circuit branches. part goingA by way of wire 16a, solenoid valve 9 and wire 11 to the panel 55 whereas wire 18h goes directly to the lpanel 55.

The wire 16b` supplies power to the ignition t means and its control whereas the wire 11. goes to the limit controls which form a part of such heaters. 'I'he wire 18 is a common return wire.

- The heater 35for the aft cabin may well take the same form as the heater 2,4 for the forward cabin. Fuel is vsupplied to the heater `35 by a fuel supply pipe 8|.A Located in this fuel supply pipe 8| is a modulating valve 82 and a solenoid on and off valve 93. The modulating valve, 82 is operated by a motor mechanism 8,4 that includes a crank arm 85 which is connected to the valveoperating arm 86 by a link ,91.` The modulating motor 84 further includes an internal balancing contact nger 89 and associated switch operating member 90 that in turn operates ka snap switch 9|, similar to the snap switch 64 of the motor mechanisrn` 58. When snap switch'9l is closed, it energizes a relay coil 92 by a circuit as follows: line wire 93, snap' switch 9|, wire 94 and relay coil 92 to thev other line wire 95j. When the relay coil 92 is energizedit attracts an armature `9B that in turn moves a switch arm 91 into engagement with a contact 99. This completes circuits for solenoid valve 83 and to the panel 80 as follows: line wire 959, contact 98, switch arm 91 and wire |00, where the circuits branch, one part going by way of ,wire lila, solenoid valve 83 and wire (0| to the panel 80, whereas'the other part goes directly to the panelt by wireiilb. Wire |02 is the commony returnwire. y

In' connection withthe apparatus as thus far described, the right and left-hand air compressors I3 and i6 may be'driven in any of the usual manners, as by being directly jgeared to the aircraft engine or engines. Furthermore, the output of these compressors may likewise be controlled by controlling thel amount of air nowing into or delivered by thev compressors. `.Such a system of pressurizing cabins and of'manually controlling the capacities of the compressors so as to maintain desired pressure conditions within the cabin or cabins of an aircraft has been used heretofore. Further, by properly sizing the ducts connecting the compressors with the forward and Til asy desired so as to maintain predetermined pressure conditions within the forward and aft cabins regardless of the laltitude at which the aircraftis dying. This may be done, for example,

aft cabins in accordance with the size and heat loss of such cabins, the air can be distributed to these cabins in a manner to maintain both of them at desired pressures and so as to distribute the heat of the compressed air between them in the ratios desired.

Whenever the temperature' of the compressed 'air is greater than that needed to maintain desred temperature conditions,the compressed air may be cooled by variably positioning the dampers |8 and 30 of the right and left-hand after coolers |1 and 28. Further, in the event the heat of the compressed air is insufficient, the auxiliary heaters 24 and 35 may be brought into operation to supply the additional heat needed. The output of the heaters may be modulated by means of the modulating valves 5,1 and 82. However, in order to obtain any supply of fuel whatsoever, the associated series connected solenoid valves 9 and 83 must be opened. Since these particular. heaters must either be off or be started at approximately,15% capacity, the switch operators 63 and 90 are so arranged that the associated snap switches 64 and 9| are not operated until the corresponding modulating valves 51 and 82 have opened to such an extent as to supply 15% of the total fuel supply. When the valves have been moved to such positions, the snap switches are operated whereupon the solenoid valves 58 and 83 open. This places the heaters in operaton. In this manner, temperature conditions within the forward and aft cabins may be maintained as deis normally primarily 'utilized for pressurizing the cabins may first be used before any auxiliaryl heatfrom the heaters 24 and 35 is utilized. The control system by means of which the right and left-hand after coolers and the auxiliary heaters 24 and 35 is controlled will now be explained in detail.

Turning now to Fig. 2, the modulating mechanism 84 of the modulating valve 82, in addition to including the parts heretofore described, also includes a split-phase motor comprising the rotor |05'and the usual associated windings |06, i01. The rotor |05 positions the crank arm 85 and the balancing Contact finger 89' through a suitable gear train |08. The balancing contact nger 89 cooperates with a balancing resistance |09. Similarly, the motor mechanism 38 for the righthand after cooler includes a split phase motor having a rotor H0 and the usual windings and ||'2. The rotor H0 positions the crank arm 39 and the balancing contact finger 52 through a suitable gear train H3. Thecontact nger 52 cooperates with a balancingy resistance M4. In like manner, the modulating motor 53 for the left-hand after cooler includes a split phase motor having a rotor H5 vand the usual windings H6 and ||1. The rotor H5 drives the crank arm 5,0 and the balancing contact finger 45 through a suitable gear train H6. The balancing contact finger 45 cooperates with a balancingfresistance H9. Likewise, the motor mechanism 58 for the modulating valve 51 includesa split phase motor having a rotor |20 and the usual windings |2| and |22. The rotor |20 drivesathe crank arm 69 and the balancing contact finger 62, as well as the switch operating member 63, through a gear reduction train |23. The balancing contact nger 62 cooperates with a balancing resistance |24.

The balancing resistances |09, ||4, I9 and |24 are all connected in series and constitute a-portion of a single resistance bridge circuit. This series circuit is as follows: wire |30, balancing resistance |09, wire 3|, wire |32,ba1ancing resistance ||4, wire |33, wire |34l balancing resistance ||9, wire |35, wire |36, balancing resistance |24, and wire |31. The resistance bridge includes .the usual input or power supply terminals, shown at 42 and 43, by means of which alternating current is supplied to the bridge. One of the bridge output terminals is indicated at 44 and comprises the pivoted end oi a contact arm |38 which engages a variable resistance |39. This constitutes a calibrating resistance for originally balancing the system at a desired point. The other bridge output terminal selectively comprises some one of the balancing contact fingers 89, 52, 45 or 62, as the case may be, since these contact fingers are selectively connected into the circuit in a manner which will be described hereinafter. Whenever any one of these contact fingers is connected into the circuit, it is connected to the terminal indicated at |40, and therefore in the explanation to follow the terminal |40 will be considered as the other bridge output terminal. The upper righthand leg of the bridge is disposed between the bridge input terminal 43 and the bridge output terminal 44 and comprises a fixed resistance |4| which is connected to the input terminal 43 by a wire |42 and further includes that portion of the calibrating resistance |39 located to the right of the contact finger |38, to which the fixed resistance |4| is connected by a wire |43. The lower right-hand leg of the bridge circuit includes varying portions of the balancing resistances |09, I4, ||9 and |24, depending upon which of the associated balancing contact fingers is connected into the circuit at any particular time and also depending upon the position of such contact finger. This lower right-hand leg further includes a fixed resistance |44, one end of such resistance being connected to wire |30 by a wire |45 and the other vend thereof being connected to the bridge input terminal 43 by a wire |46. In a similar manner, the lower left-hand leg of the bridge circuit includes some portion of the series connected balancing resistances and a fixed resistance |41, one end of which is connected to wire |31 by a wire |48 and the other end of which is connected to the bridge input terminal 42 by a wire |49. The upper left-hand leg of the resistance bridge circuit includes a number of thermally responsive variable resistances which are selectively connected into the circuit under varying conditions. These connections will be described in detail hereinafter. These variable resistances include temperature sensitive resistances |50, and |52. All of these temperature sensitive resistances are of the usual type in which the resistance increases upon temperature increase. The temperature sensitive resistance |50 responds to the temperature of the air being discharged into the forward cabin and is therefore shown, in Fig. 1, as being located directly in front of the outlet 26. The temperature sensitive resistance I 5| responds to the temperature of the air being delivered to the heater 24 for the forward cabin and is therefore shown, in Fig. 1, as contacting the duct 23 leading to the auxiliary heater 24. The temperature sensitive resistance |52 responds to the temperature of the air discharged into the aft cabin and is therefore shown in Fig. 1 as being located directly in front of the outlet 31. In addition, this leg of the bridge includes a temperature operated variable 5 resistance comprising a resistance |53 and a cooperating contact |64 which lis positioned by an arm I 55 that is in turn caused to move back and forth by a temperature sensitive element |56, herein shown in the form of the well known bellows. This thermostatically or temperature operated variable resistance responds to the temperature within the forward cabin as distingu'ished from the temperature of the air being discharged thereinto. If desired, the resistance |63 may be varied manually instead of thermostatically.

Associated with the bridge circuit and with the windings of the various motors heretofore described, is an electronic amplifier and transformer unit |58. The amplifier may be of any conventional type in which the output voltage has a definite phase relation to the signal voltage. 'Iypical amplifiers of this type are shown in the `Anschutz-Kaempfe Patent 1,586,233 and the Chambers Patent 2,154,375. The amplifier and transformer unit |58 is supplied with alternating current which supply is herein indicated by the wires |59 and |60. The transformer portion of the unit |58 further applies power to the bridge input terminals 42 and 43 in such manner as to apply an alternating potential thereto which is fixed in phase with respect to the main supplies |59 and |60. These connections to the bridge input terminals are by wires |6| and |62. The outa put terminals 44 and |40 of the bridge circuit are connected to amplifier input terminals by wires |63 and |65. In addition, the amplifier and transformer unit |58 is provided with three terminals for connection tothe motor or motors. These are indicated at |61, |68 and |69. 'I'here is a constant source of potential across the common or return terminal |68 and the terminal |69, which potential is fixed in phase with respect to the power supply |53 and |60. The terminal |61 onLy has potential applied thereto when the bridge is out of balance, and this potential varies in phase depending upon the manner in which the bridge is unbalanced, as will be more fully described hereinafter.

It has been stated above that the various balancing contact fingers of the four motor mechanisms are selectively connected to the bridge. This is accomplished by a program switching mechanism, located at the lower part of Fig. 2, 55 which will now be described. This switching mechanism includes a split phase motor having a rotor and the usual windings |1| and |12. The winding |1| is directly connected to the motor terminal |69 of the amplifier |58, and the so winding |12 is connected thereto through a condenser |13. These circuits are as follows: terminal |69, wire |14 and wire |15 at which point the circuit splits, one portion going to one end of winding 1| by way of wire |16 and the other portion going to one yend of winding |12 by way of a wire |11 and condenser |13. The opposite ends of the windings |1| and 12 are both directly connected to the common terminal |68 of the amplifier |58 by'wires |18, |19 and |80. 70 As a result, the windings |1| and |12 are constantly energized but one of these windings is 90 degrees out of phase with the other by reason of the insertion of condenser |13 so that the rotor |10 is constantly rotated, as is well known 75 in the split phase motor art. Rotor |10 drives mais? a cam shaft |82 through a sui-table gear train |83. The motor speed and reduction gear train `|83 may be so correlated, for example, as to cause the` cam shaft |82 to make fifteen revolutions per minute or one revolution every four seconds. Cam shaft |82 drives four cams |84, |85, `|86 and |81. The cam |84 is provided with` a raised portion extending substantially over one quarter of its circumference as shown at |88. The raised portion |88 cooperates with a, cam

`follower |88 that operates four switches |88, |8|.

|82 and |98 to closedl circuit position upon raising of the cam follower |88 by the raised portion |88. The switches |88, |9|, |92 and |83 therefore are closed during one quarter of each revolu- .tion ofthe cam shaft |82. In other words, these switchesare closed one second out .of every four with a raised portion 28| that cooperates with a cam follower 282 which operates fourswitches 288, 284, 285 and 286. The 'raised portion 28| is so placed that it raises its cam follower 282 at the time that the cam follower |86 rides off o'f the raised portion |85 of cam |85. Similarly, the cam |81 is provided with a raised portion 281 that cooperates with a cam follower 288 which in turnv operates four switches v288, 2|8,

. 2|| and 2|2. The raised portion 281 is so posi- ,L

tioned that it raises its cam follower 288 at the time that the follower 282 rides off of the raised portion 28| of cam |86. As a result, the four sets of four switches are repeatedly closed in sequence for a period of one second and this sequence is repeated over and over again under the constant energization of the motor comprised by rotor |18 and the windings |1| and |12.

Each and every one of the eight windings of the four modulating motors has one of its ends connected to the common terminal |68 of the amplifier |58'by means of wires 2|5, 2|6, 2|1, 2|8, 2|8, 228, 22|, |18, and wire |88 to said terminal |68.

Winding |86 of motor mechanism 84 is intermittently connected to terminal |68 of the amplifier |58 through a condenser |64, and switch |88 by a circuit as follows: terminal |68, wire |14, condenser |62, wire 222, wire 223, switch |98, and wire 228 to the upper end of Awinding |86. The winding |82 ci the same motor mechanism 84 `is vconnected to terminal |61 of amplifier |58 by wire 225, wire 231, wire 226, switch |8|, and wire221 to one end of winding |81.

' In like manner, windings ||6 and |2| are each selectively connected. to the terminal |68 through the condenser |64 and through their respective switches |61, 283 and 288 by a wire 228 `which. joins wire 222 `and. additionally by wires 229 to235, inclusive. Also, 'the windings ||2, |1 and |22 are each 'selectively connected to the terminal 61 through their respectiveswitches |88, 284 and 2|||by a wire 298 which connects to wire 231 and: additionally by wires 238 to 245, in-

clusive. v

The balancing contact finger 8,8 of motor mechanism 84 is connected tothe bridge output terminali by wire 258, switch |92, wire wire 25,2, and wire 253. Similarly, the balancing contact linger 52 of motormechani'sm 38 isconnested to bridge output terminal |48 by wire 264,

switch |88. wire 255, wire 252, andwire 253. In like manner, the balancing contact finger of motor mechanism 53 is connected to bridge output terminal |48 by wire 256, switch 285, wire 251 and wire 253. Further, the balancing contact iinger 62 of motor mechanism 58 is connected to bridge output terminal |48 by wire 258, switch 2| I, and wire 258.

The connections of the `various variable resistances and other parts included in the upperleft-hand leg of the bridge circuit as well asvthe connections of the remaining switch of each of the four sets of switches, namely the switches |83, 288, 286 and 2|2 will be brought out in 'the detailed description of the operation of the system Operation For the purpose of more clearly explaining what happens in the system from an electrical standpoint, let it be assumed for the time being that there is always heat available from the compressors I3 and I4 irrespective of the altitude at which the aircraft is ilying. Further, with the parts in the position shown in Fig. 2, a condition is represented wherein the aircraft is at a reasonably low altitude in temperate weather so that the temperature within the aircraft is at say degrees without there beingA any heat supplied thereto. In other words, the outdoor temperature conditions are such that no heat is need in the aircraft. It will be noted, that the group of switches controlled by cam `|84 has just been closed since the raised portion |88 of such cam has just begun to move underneath the cam follower |88. Under these conditions, the windings |88 and-|81 are connected to the amplier |58 by the circuits previously described and additionally, the balancing contact finger 88 is connected to the bridge output terminal |48 by the wiring heretofore described. Furthermore, closure of switch |83 has completed a circuit comprising the left-hand leg of the bridge circuit, as follows: from the bridge input terminal 42, to wire 265, wire 266, switch |83, wire 261, a resistance 268, a cooperating contact 268, wire 218, the aft cabin discharge controller |52, wire 21|, wire 212, resistance |38, and contact |38, to the output terminal 44 of the bridge circuit. The manual contact 268 is engaging resistance 268 at such a point that the full amount of such resistance is included in the circuit just traced. The resistance bridge circuit as a whole may be based, for example, on providing a 500 ohm bridge. Also, the aft cabin discharge controller |52 should be such that it is capable of having a control range of from, for example, 80 F. to 180 F. with an operating differentia1 of say 5 F. Under these conditions, and remembering that the temperature of the outside atmosphere and therefore of the aft cabin, as weil as any air owing over the discharge controller |52, vas will presently he explained,` is at 80, then the resistance of con- ,troller |52 at a temperature of 80 plus the the balancing contact finger 88 is at the extreme right-hand end of balancing resistance |89, so that the lower left-hand leg of the bridge comprises the nxed resistance |41 as well as all of the balancing resistances in series, and the lower right-handleg of the bridge includes only the fixed resistance |44. In order to obtain a balance under these conditions, and wherein each of the four balancing resistances has a resistance of substantially 400 ohms, there is provided manually operable shunt resistances for each of the balancing resistances so that their effective resistances may be adjusted to a much smaller value. This shunt resistance for balancing resistance |09 is indicated at 213 and shunts the balancing resistance |89 by a circuit as follows: starting at the right-hand end of resistance |89, then by way of wire |38, a wire 214, shunt resistance 213, a wire 215, a wire 216, and wire |3| to the left-hand end of balancing resistance |09. The shunt resistances for the remaining three balancing resistances and the wiring therefor is as follows: starting with the left-hand end of balancing resistance |24, wire |31, wire 288, shunt resistance 288, wire 290, wire 28|, shunt .282, wire 283, wire 294, wire 285, shunt 296, and wire 291 to wire 216. Each of these shunt resistances is manually adjustable and may be ad- Justed to, say, flve or six ohms. These resistances also determine the over-all temperature diierential or temperature change required at the controllers for the system to operate.

throughout its complete cycle. Incidentally, the three fixed resistances of the bridge |4|, |44, and |41 may, for example, each be of 500 ohms and the calibrating resistance |39 may, for example, be ohms.

Since the bridge is in balance with the parts in the position shown, no power will be supplied to terminal |61 as is fully brought out inthe previous description. Only winding |06 of the motor will then be energized wherefore rotor |05 will remain stationary and the parts will remain in the position shown.

After the passage of one second, the cam |84 will open its' group 0f switches and the cam |85 will close its group of switches. The motor windings |06 and |01 and the balancing contact finger 88 of the modulating mechanism 84 are therefore disconnected and likewise the circuit through the aft cabin discharge controller |52 is broken. However, the motor windings and ||2 of the motor mechanism 38 are now connected to the amplier |58 and the balancing contact finger 52 is connected to the bridge output terminal |40 by the circuits previously traced. In addition, the switch 288 operated by cam |88 sets up a new circuit comprising the upper left-hand or controlling leg of the bridge. This new circuit is as follows:` bridge input terminal 42, wire 265, wire 211, wire 218, wire 218, switch 280, wire 288, wire 28|, switch arm 12, contact 13, wire 282, wire 283, forward cabin discharge controller |50, wire 284, wire 286, resistance |53 of the cabin temperature controller, contact |54 thereof, arm |55, wire 286, wire 212, the left-hand portion of resistance |38 and contact finger |38 to the output terminal 44. -Inasmuch as the cabin temperature is 80 or thereabouts, the thermostatically operated contact |54 is at one extreme end of resistance |53 so that all of such resistance is in the circuit. This it will be noted is in series with the temperature sensitive resistance |50 which re- 12 resistance of these two resistances under such temperature conditions should be substantially 500 ohms plus the effective resistance of the three rebalancing resistances |24, ||8 and ||4. Since the bridge is in balance under these conditions, only winding of the modulating motor mechanism 38 is energized wherefore rotor ||8 remains in a stationary position. As a result, the damper I8 of the right-hand after cooler remains Wide -open so that a full flow of outside air ows through switches. Closure of the lower two switches connects the windings |I6 and ||1 of the motorized mechanism 53 to the amplifier |58. Closure of the switch 205 connects contact finger 45 to the bridge output terminal |48. Closure of switch 206 establishes a further circuit for the controlling leg of the bridge through the forward cabin discharge controller |58 and the cabin temperature operated resistance as follows: from bridge input terminal 42, wire 265, wire 211, wire 218, wire 300, switch 208, wire 30|, wire 28|, switch arm 12 contact 13,wire 282,wire 283, resistance controller 50,wire 284, wire 285,resistance |53,contact |54, arm |55, wire 286, wire 212, the left-hand portion of calibrating resistance |88, contact |38, and bridge output terminal 44. In other words, under this particular set of conditions, the controlling leg of the bridge circuit is exactly the same as that just described in connection with motor mechanism 38. However, whereas the lower left-hand leg of the bridge formerly included the three balancing resistances I4, ||8 and |24, it now only includes two of them, namely balancing resistances ||8 and |24. The lower right-hand leg of the bridge on the other hand now includes both balancing resistances |03 and ||4 where before it only included the one balancing resistance |08. Since the bridge was formerly in balance, it is obvious that it is now out of balance. In other words, since there is less resistance to the left of bridge output terminal |48 than formerly, the potential of the bridge output terminal |48 is now higher than that of bridge output terminal 44. As a result, the amplifier and transformer unit |58 not only energizes motor winding ||6.

ninety degrees out of phase with the power supply in view of condenser |64, but it also energlzes motor winding ||1 either in phase with the power' supply or 180 degrees vout of phase therewith, depending upon the direction of unbalance of the bridge. When the bridge is unbalanced in one direction, that motor winding which is not constantly energized is energized with a. current which is in phase with the power supply and when the bridge is unbalanced in the other direction, that motor winding is energized by current which is 180 degrees out of phase. Therefore, the one motor winding either leads or lags the other degrees. For the purpose of this discussion, let u s. assume that with an unbalance of the type which we now have wherein the potential of bridge output terminal |48 is higher than that of bridge output terminal 44, the motor winding 13 I|1 is energized by a current which leads that of motor winding II8 by 90 degrees. The rotor ||5 ywill therefore rotate in such a direction, or try to rotate in such` a direction, that gear train I|8 will try to drive contact finger 45 to the right. However, since the contact finger 45 is at the end of balancing resistance II 8, in which position the shutter 30 oi' the left-hand after cooler is wide open, it is at its limit of travel and the motor will merely remain stationary since it will' be stalled under such conditions. It will be obvious that in order to rebalance the-bridge more resistance would have to be placed in the lower left-hand leg thereof and this is what the motor mechanism 53 tries to do but it cannot accomplish its objective because it is already at the end of its movement. As a result, the left-hand after cooler damper 30 remains in its wide open position and the air being delivered by the left-hand compressor is cooled to the greatest extent.

After the period of a second. the cam |85 permits its associated switches to open which disconnects contact linger 45 from bridge output terminal |40 and also disconnects the motor windings ||5 and ||1 from the amplier |58. In addition, the last named circuit for the control leg of the -bridge circuit is interrupted. At the same instant, the cam |81 closes its associated switches.` Closure of switches 208 and 2|0 connects motor windings |2| and |22 to the amplifier |58. Closure of switch 2| I connects the contact nger 52 to the bridge output terminal |40. These circuits have been previously traced. In addition, `closure of switch 2|2establishes a further controlling leg bridge circuit which includes the same resistance elements as heretofore described. This circuit is as follows: starting with bridge input terminal 42, wire 255, wire 211, wire 302, switch 2|2, wire 303. wire 283, forward-cabin discharge controller |50, wire 284, wire 285, resistance |53, contact |54, arm |55,

. wire 286, wire 212, the left-hand end of calibrating resistance |38, contact |38, and bridge output terminal 44. `Hero again, we have the same circuit in the controlling leg of the bridge as in the two previous instances. However, the bridge output terminal |40 is now connected to the contact finger 52 so that the lower left-hand leg of the bridge has still less resistance since it now includes only the single balancing resistance |24. As a result, the potential of bridge output terminal |40 will be still higher with respect to bridge output terminal 44 than it was in the last instance wherefore the motor mechanism 58, in trying to rebalance the bridge, will try to move the contact finger 62 to the right. yHere again, this is impossible since it is already at its limit of movement, wherefore the motor will remain stationary under a stalled condition, and the modulating valve 51 for the forward cabin heater 24 will remain in its full closed position.

So long as the temperature conditions remain the same the system will continuously go through its cycle sequentially connecting the various contact fingers into the bridge circuit but no change in the position of any of the parts will occur.

Let us now assume that the' aircraft begins climbing and as a result the temperature outdoors becomes cooler. The temperature of the aft cabin discharge controller |52 will drop slightly and its resistance will therefore decrease. The potential of bridge output terminal 44 will now become closer to that of bridge input terminal 42 (in other words the potential of bridge output terminal 44 increases) and, when the program switching mechanism is in the position shown, the potential of bridge output terminal |40 (which under such conditions is connected to the contact finger 83) has been unchanged. The potential of bridge output terminal 44 is now higher than that of bridge output terminal |40. This is the reverse of the situation discussed above so that the amplier |58 will now supply to the motor winding |01 a current which lags that oi the winding |05. Rotor |85 now drives contact arm 09 to the left. This reduces the resistance in the lower left-hand leg of the bridge and thereby raises the potential of bridge output terminal |40. When this potential again equals that of bridge output terminal 44, the amplier will no longer supply current to the motor winding |01 and the motor will cease rotating. The modulating valve 82 for the aft cabin heater 35 has thus been opened somewhat. Let us assume that this opening of the valve 82 for the aft cabin heater 35 is less than 15 per cent so that the snap switch 9| remains open. Underthese conditions, although the bridge has been rebalanced, still no heat is furnished to the aft cabin by its auxiliary heater. The cam |85 now closes its switches so that the forward cabin discharge controller and the associated cabin thermostat now control the bridge and the motor mechanism 38 is connected into the circuit. This aforementioned drop in temperature does two things in connections with the forward cabin. The temperature of the forward cabin discharge controller |50 drops slightly so that its resistance decreases. Also, the forward cabin temperature itself decreases so that the thermostatic element |55 contracts and contact |54 moves to the right along resistance |53 thereby removing some of the resistance from the circuit. The controlling leg of the bridge therefor has had its resistance decreased in two different manners. As a result of this decrease in resistance, the potential of bridge output terminal 44 is higher than that of bridge output terminal |40 which is now connected to the contact finger 52 of :motor mechanism 38. It follows then that motor winding ||2 is energized with a lagging current in respect to that of winding whereupon motor rotor I0 turns in such a direction that gear train 3 drives contact finger 52 towards the left along balancing resistance ||4 and simultaneously partially closes damper I8 of the right-hand after cooler. Keeping in mind that for the purposes of the present discussion we are assuming that there is always a certain amount of heat available from the compressors regardless of altitude, this partial closing down of damper I8 reduces the ow of outside air through the right-hand after cooler so that the temperature of the air being delivered to both the forward cabin and the aft cabin is increased. This increase in temperature of such air will raise the temperature of the forward cabin discharge 'controller |54 and thereby increase its resistance. However, it does not necessarily raise to any substantial extent the temperature within the cabin itself. It may just be suflicient to oliset the increased heat loss therefrom. The ultimate result is that the bridge ls again rebalanced when contact linger 52 has moved to some predetermined position along balancing resistance ||4 in a left-hand direction and more heat is being delivered to the cabins under this set of conditions. With the bridge rebalanced, and this will take place very quickly in view of the electronic amplifier |58 which operates very rapidly, the winding ||2 will be deenergized by the amplier |58. Therefore, as a result of this small temperature drop, less cooling air is flowing through the right-hand after cooler so that more heat is being deliveredto the cabin and the control point of the forward cabin discharge controller I 50 has been raised since the amount of resistance in series therewith has been decreased by the action of the forward cabin thermostat.

Again, after the passage of one second, the cam |85 permits its associated switches to open and the cam |88 closes its associated switches. 'The potential of bridge output terminal |40 is now that ofthe contact linger 45 and the controlling leg of the bridge is that including the forward cabin discharge controller |50 and the forward cabin thermostat. Assuming that condltions have not changed further, it will be evident that the potential of bridge output terminal |40 is still higher than that of bridge output terminal 44 since contact nger 45 is now connected to the bridge Output terminal |40 and the bridge was in balance just a moment ago when the fingerl 52 was connected to bridge output terminal |40 and such finger 52 had only moved a little ways to the left along balancing resistance I|4. The motor winding II1 will again be energized with a current which leads motor winding IIS and the apparatus will attempt to move contact finger 45 to the right but will be unable to do so since the motor stalls under these conditions. Therefore, the damper 30 of the lefthand after cooler remains in wide open position.

Subsequently, ythe cam I81 operates its switches to connect contact nger 82 to the bridge output terminal |40. The unbalance of the bridge will be even greater than when contact finger 45 was connected to the bridge output terminal |40 and again, winding |22 will be energized with a current which leads that of winding |2| and an attempt will be made to further close the already closed modulating heater valve 51, but this will be unsuccessful and the motor will be stalled.

As the aircraft continues to climb or as the outdoor temperature continues to fall for any reason so that more and more heat is demanded within the forward cabin, both auxiliary heaters will remain ol but the damper I8 of the righthand after cooler will continue to close more and more until it is fully closed. When it has become fully closed; the contact nger 52 will be at the extreme left-hand end of balancing resistance II4. Now, if the forward cabin still demands more heat and further unbalances the bridge, it will be evident that motor mechanism 38, having reached its opposite extreme position, can do nothing further towards rebalancing the bridge. As a result, the next time contact finger 45 is connected to bridge output terminal |40, its potential will be lower than that of bridge output terminal 44. Therefore, for the first time, the motor winding I I 1 will be energized with a current which leads that of motor winding |I6 and rotor ||5 will turn in the direction opposite to that which it had theretofore attempted to rotate. This drives contact finger 45 along balancing resistance ||9 towards the lefthand end thereof and simultaneously closes ofl' the damper 30 of the left-hand after cooler so that less of the cold outside air cools the hot compressed air. Such movement will continue until contact nger 45 is in such position on balancing resistancerl I9 as to again rebalance the under such conditions will still remain stationary in the position shown since the balance point for the bridge is now within the range of balancing resistance IIS.

As it continues to get colder. and colder outside and as the forward cabin temperature therefore continues to drop, the forward cabin temperaturethermostat will continue removing resistance from in series with the forward cabin discharge controller |50 so as to continue raising its control point so that hotter and hotter air is delivered to both the forward and aft cabins. When the heat loss becomes great enough, the contact flnger 45 will move to the extreme lefthand end of balancing resistance I I9 under which conditions the damper 30 will be completely closed so that both after coolers are completely shut off. The system is therefore using the entire heat output of the right and left-hand compressors. If this heat output is insuiilcient to maintain the temperature of the air being discharged into the forward cabin at that point for which such controller has been set by the action of the forward cabin thermostat, the resistance in the control leg of the bridge at the time that the modulating motor mechanism 58 for the forward cabin auxiliary heater is connected into the bridge circuit will become still smaller. The potential of bridge output terminal |40 under such conditions willrise above that of bridge output terminal 44 and motor winding |22, for the rst time, will become energized with a current which leads that of motor winding I2I. Contact finger 62 therefore moves to the left along balancing resistance |24 in order to rebalance the bridge circuit. Modulating valve 51 in the fuel supply for the forward cabin auxiliary heater 24 therefore begins opening. When the demand is great enough so that the valve 51 opens at least 15 per cent, the switch operating member 53 will 0perate snap switch 54 to its closed position to energize relay coil in the manner heretofore described. Closure of switch arm 10 into engagement with contact 1I energizes the sloenoid fuel supply valve 58 and places heater 24 into operation.

The auxiliary heater 24, as explained, is not and cannot safely be brought into operation except at a minimum of 15 per cent of its full capacity. Since this heater has quite a large capacity, 15 per cent of such capacity results in the delivery of considerable heat to the forward cabin; in fact, too much heat to prevent the temperature from overshooting. However, energization of relay coil 65, as heretofore explained, moves switch arm 12 away from contact 13 and into engagement with contact 14. As a result, certain new circuits are set up in the controlling leg of the bridge. Now, when the cam |85 closes its switches so as to connect the right-hand after cocler control motor 38 into the system, it is no `longer controlledvby the forward cabin discharge controller but is now controlledn by the forward cabin heater intake controller |5| which responds to the temperature of the air being delivered to the heater as distinguished from responding to the temperature of the air being discharged by the heater. This control circuit is as follows: starting with the bridge input terminal 42, wire 255, wire 211, wire 218, wire 219, switch 200, wire 280, wire 28|, switch arm 12, contact 14, wire 305, forward cabin heater intake controller |5|, wire 306, wire 285, resistance |53, contact |54, arm |55, wire 288,y

wire 212, the left-hand portion of calibration resistance |39, contact |38, and bridge output terminal 44. The resistance of the forward cabin intake controller is so arranged that it demands a somewhat lower temperature than the forward cabin discharge controller |50. Therefore. when the forward cabin heater intake controller is thus placed in control of the motor mechanism 38, which motor mechanism has formerly been in the position in which the right-hand after cooler damper |8 was fully closed, the balance of the ridge is changed so that the motor mechanism 38 backs up somewhat towards the position shown and thereby somewhat opens up the d amper I8 of the right-hand after cooler. Some outside air is now used to cool the temperature of the compressed air whereby the temperature of the air delivered to the forward cabin auxiliary heater 24 is reduced to compensate for the initial relatively large output at which such heater must be started. Simllary, the motor mechanism 53 for the left-hand after cool-er is now controlled by the forward cabin intake controller |5|. This controlling circuit of the bridge is as follows: starting with bridge input terminal 42, wire 265, wire 211, wire 218, wire 300, switch 206, wire 30|, wire 28|, switch arm 12, contact 14, wire 305, controller |5|, wire 306, wire 285, resistance |53, contact |54, arm I 55, wire 286, wire 212, resistance |39, contact |38, and bridge output terminal 44.

As a result, the left-hand after cooler damper 30 may also begin to reopen. Of course, it should be noted that any resistance value which causes the motor mechanism 38 to move its contact nger 52 away from its left-hand end will, in view of what has been said heretofore, when applied to the motor mechanism 53 be such as to cause it to move its slider 45 to its complete right-hand position. Therefore, whether ornot each of these motor mechanisms will be moved under the inuence of forward cabin heater intake controller |5| and the extent to which motor mechanism 53 will be moved if` motor mechanism 38 does not move at all, depends upon the resistance value of the controller |5|. This.in turn depends upon the amount of temperature diiference or the difference in the temperature settings of the intake controller 5| and the discharge controller |52.

This further depends in turn upon how much overshooting will take place upon the initiation of operation of forward cabin auxiliary heater 24 at per cent of its capacity since it is the intention, as has been accomplished in actual practice, to merely compensate for whatever overshooting may take place and this of course will vary with a number of factors including the minimum capacity allowable in initiating heater operation, the total capacity of the heater, the size of the cabin being heated, etc. However, in any event, the intake controller resistance |5| is so chosen that at least one of the after coolers will have its'shutter open somewhat so as to compensate for the initial blast of heat delivered to the forward cabin upon bringing into operation the forward cabin auxiliary heater 24.

If the temperature continues to'drop, the forward cabin thermostat will remove further resistance` both from in series with the forward cabin discharge controller |50 and the forward cabin heater intake controller |5|. The control points ofeach of these controllers will thereby be raised. Raising of the control point of the forward cabin discharge controller I 50 will of course cause the heater modulating valve 51 to open wider and wider until full capacity of the heater is utilized, if this be necessary. Raising of the control point of the forward cabin heater intake 18 controller |5| will result in reclosing on of one or the other of the after cooler dampers I8 and 30, depending upon whether both were opened initially or if only one of them was opened initially.

As to the aft cabin. so long as the heat of the compressed air as controlled by the dampers on the right and left-hand after coolers was suilicient to maintain desired conditions within the forward cabin, and due to the division of such heated air between the two cabins, the aft cabin would remain under reasonably accurate control until such time as the auxiliary heater for the forward'cabin was brought on. f This would indicate that there was insufficient heat for the aft cabin also. In order to obtain more heat for the aft cabin under such conditions, the pilot can operate the manual contact 269 along the resistance 268 so as to remove as much of such resistance as desired. This action raises the control point of the aft cabin controller |52. In other words, it reduces the total resistance in the controlling leg of the bridge circuit when the motor mechanism 84 is connected into the system with the result that higher and higher discharge temperatures must be maintained to the aft cabin in order to maintain tl system in balance. In order to obtain such higher discharge temperatures and rebalance the bridge, the contact linger 89 must move along balancing resistance |03 towards its left-hand end. When it has moved 15 per cent of its total movement, the switch operating member 90 operates the snap switch 9| to energize relay coil 92 whereupon the solenoid fuel valve 83 is opened and the aft cabin auxiliary heater 35 is turned' on.

In this manner, the aft cabin temperature can be maintained by the pilot through his adjustingA the manual resistance in association with the aft cabin controller |52. Of course, the aft cabin could be provided with an entirely separate control system of its own corresponding to the control system for the forward cabin.

It should also be understood that tne control point of the aft cabin |52 could be automatically adjusted by an aft cabin thermostat similar to the forward cabin thermostat. On the other hand, if full automatic control is not desired, the forward cabin thermostat could be replaced by a manual controller such as used 1n connection with the ait cabin controller |52.

It is believed it will be obvious that the reverse action will take place upon temperature increase due to a rise in temperature in the outside air either by reason of atmospheric conditions or by reason of the aircraft going downwardly to a lower altitude.

The operation as described above correctly sets forth what would happen on a gradual lowering in temperature and assuming that the air compressors always were delivering some heat. However, since in actual practice it is not the intention to operate the air compressors so as to maintain a pressure within the cabin equivalent to standard atmospheric pressure at sea level, but instead only to maintain a pressure in the cabin equal to standard conditions, say at 8,000 feet, there will be no heat available from the air compressors until an altitude of 8,000 feet is reached.

Although the electrical sequence and operation of the parts would be unchanged, the following is an example as to what would actually happen under normal ight conditions wherein the air compressors were not actually used to tude were reached. Assuming that the plane took oif at or about sea level and in a temperate climate so that the outdoor air temperature were 80 degrees or above, the parts of the mechaniSm would all be in the position shown with both after cooler shutters wide open and both auxiliary heaters off. As the aircraft gains altitude and before it reaches an altitude of 8,000 feet sovthat the air compressors are still incapable of furnishing any heat, it is obvious that the outdoor temperature will fall below 80". As a result, cold outside air will be supplied to the cabin, and in addition, the heat loss from the cabin to the outside atmosphere will cause the cabin temperature to drop. As brought vout above, the first reaction to this drop in temperature will be a sequential closing down of the right-hand and then the left-hand shutters of theA right and left-hand after coolers. This will heat of compression. When this is insuflicient. the auxiliary heaters will again be brought into operation. As the plane continues to descend the available heat of compression from the air compressors will be less and less until, at some altitude around 8,000 feet, it will become negligible or` entirely gone. yUnder such conditions. the heat losses from the cabins must again be entirely supplied by the auxiliary heaters. As the plane continues to descend and if it is descending in a temperate climate where the temperature at reduce the amount of cold outside air flowing through the right and left-hand after coolers but, since the air compressors are not furnishing any heated air'anyway, there will be no actual result in the direction of raising the temperature of the cabin. When it becomes suiliciently cold outside and an altitude of 8,000 feet has not been reached, the temperature in the forward cabin will have fallen to such an extent that the auxiliary heater 24 will be brought on. Also, the temperature in the aft cabin may have fallen to such an extent that the pilot nds it necessary to adjust the manual controller or manual control resistance contact 269 so that the auxiliary heater 35 for the aft cabin will be brought into operation. Y Y

As the aircraft continues to climb and rises above 8,000 feet the right and left-hand compressors will be brought into operation so as to maintain the desired pressure within the cabin. The compression of this air will likewise furnish heat. A point will therefore be reached at some ground level and some distance thereabove is 80 or higher, then nally the auxiliary heaters will be completely turned oif and no heat will be necessary in either of the cabins. f'

In this manner, it will be noted that the aux iliary heaters are used only when necessary. In so far as is possible, the heat required by the cabins is supplied by the air compressors. However, whenever the air compressors do not furnish suilicient heat, then the auxiliary heaters are placed into operation.

From the foregoing, it will be seen that in connection with the forward cabin, I have disclosed a completely automatic control system wherein the temperature in such cabin is automatically maintained at a predetermined value or within a predetermined range of change by utilizing auxiliary heating means whenever necessary and by utilizing, to the fullest extent possible, whatever heat is available by reason of maintaining desired pressures within such cabin. Furthermore, I have disclosed automatic means for preventing overshooting when heat is available from the air compressors but in insufficient quantity so that an auxiliary heater must be placed into operation, but which auxiliary heater cannot be initially started except at some relatively high percentage of its total capacity. Specifically, this is accomplished by not utilizing the full amount of heat being genaltitude wherein there is suiilcient heat being furnished to the cabins by the right and lefthand compressors (through the after coolers whose shutters are completely closed) that the temperature in the cabins will rise higher than desired. The automatic control system for the forward cabin will therefore begin closing offv the fuel valve for the auxiliary heater 24 for the forward cabin. By manual adjustment, the pilot can accomplish the same result in' connection with the aft cabin auxiliary heater 35. As the aircraft continues to rise, more and more heat will be produced by the compressors in maintaining the desired pressures within the cabins so that the auxiliary heaters will be used less and less. A condition may ultimately occur in which the compressors will be furnishing so much heated air in maintaining desired pressure con` ditions within the cabin that the auxiliary heaters will be turned completely o. In fact. the shutters on the after coolers or at least one of them may begin to open somewhat in order to dissipate the excess heat produced by the compressors in maintaining the desired pressures within the cabins.

The reverse operation will take place as the plane begins to descend. As it descends, it is unnecessary to furnish so much compressed air to the cabins in order to maintainthe desired pressures therein. As a result, less heat will be furnished to the cabins by the air compressors. The after cooler shutters will therefore go completely closed so as to utilize all of the available erated by the air compressors. This is the only circumstance under which the heat of compression is not utilized to its fullest available capacity and in this instance some of that heat is sacriiiced towards the end of maintaining desired temperature conditions within the cabin and preventing overshooting and too frequent on-off operation of the auxiliary heater.

In respect to the aft cabin, as stated above, it could be made fully automatic in the same manner as the forward cabin temperature control. Or, if desired, an entirely separate system entirely analogous to that for the forward cabin could be used for the aft cabin.A

It should be further understood that my system' of control includes features of novelty in respect to the modulation of two or more devices upon the demands of a single controller irrespective of the type of system in which the apparatus is used. Furthermore, I have provided a novel bridge system in which the rebalancing is accomplished by a number of modulating motors all of which remain in their proper step or sequence. Many of these features of my present invention are of general utility in the motor control art. I therefore intend to be limited only by the scope of the claims appended hereto.

I claim as my invention:

1. In a temperature changing system for a space, means for supplying airto said space, said supplying means including means for heating said air, means for cooling said air, means for additionally heating said air comprising a combustion heater, means for supplying fuel to said heater including a motorized modulating valve means and a solenoid valve in series, means including a switch operated by said modulating valve means for causing operation of said solenoid valve when said modulating valve means has opened a predetermined amount, means for sequentially controlling said cooling means and said additional heating means in a manner wherein the effect of said cooling means is lrst reduced to a minimum and then the modulating valve is gradually opened but no heat is provided due to the solenoid valve being closed until the modulating valve opens enough to operate the said switch, and means operable to increase the eiect of said cooling means when said switch is operated.

y 2. In a conditioning system for a plurality of zones, means for supplying condition changing medium to all of said zones, first means for changing the condition of the medium supplied to all of said zones, means for additionally changing the condition of the medium supplied to the individual zones, means responsive to the condition of the medium discharged in each of said zones, means responsive to the condition of the medium resulting from the first condition changing means, and switching means for sequentially placing said discharged medium condition responsive means in control of the additional condition changing means for the respective zones and for placing the means responsive to said resulting condition in control of the rst condition changing means.

, 3. In a conditioning system Afor a plurality of zones, means for supplying condition changing lmedium to said zones, means for changing a condition of said medium, additional means for changing the condition of the medium supplied the individual zones, motor means for controlling n medium capable of being modulated only down to a predetermined minimum output, and a control circuit including a temperature responsive device connected in controlling relation to said temperature changers in such a manner that said first temperature changer is adjusted to its maximum output before placing said second temperature changer in operation at its minimum output, the output of said rst temperature changer then being reduced.

5. In a condition controlling system for first and second condition changers for changing a desired condition in which the second of said condition changers must initially be placed in operation at an appreciable portion of its capacity but may thereafter be modulated to its full capacity, in combination, a first condition 1esponsive device responsive to said condition as affected by both said iirst and second condition changers, means for connecting said device in controlling relation to said condition changers for graduatingly varying the effect of said first condition changer to a maximum upon an increase in demand by said device, means including switching apparatus for placing said second condition changer into operation and thereafter gradually increasing its edect, a second condition responsive device responsive to said condition as affected only by said first condition changer. and means operable as an incident to initiation of operation of said second condition changer for placing said second condition responsive device in control of said rst condition changer.

6. In a temperature control system having first and second temperature changers for serially changing the temperature of a fluid medium and in which at least said second temperature changer when initially made operative to change the temperature of said medium does so at a relatively high rate, in combination, a first temperature responsive device responsive to a temperature aiected byv both of said temperature changers in control of said temperature changers and operative to gradually vary the temperature changing capacity of said first temperature changer, then initiate operation of said second temperature changer and nally increase the temperature changing capacity of said second temperature changer, a second temperature responsive device responsive to the iiuid medium after it has been subjected to said first temperature changer but before it has been affected by said second temperature changer, and means operable as an incident to initiation of operation of said second temperature changer for placing said second temperature responsive device in control of said rst temperature changer.

7. In a temperature control system for an aircraft having a compressor for maintaining desired air pressures in said aircraft at varying altitudes, which compressor incidentally heats the air delivered to the aircraft, in combination, an auxiliary source of heat for said aircraft, which sourceof heat has a minimum temperature changing ability of substantial proportions, temperature responsive means for determining the eiect of said hot compressed air upon said aircraft, motor actuated means controlled by said temperature responsive means for gradually increasing the temperature changing effect of said hot compressed airto its maximum, and' switching means for placing said auxiliary source of heat into operation at a minimum rate and reducing the temperature changing effect of said hot compressed air below its maximum to such an extent that the overall temperature changing effect is only slightly increased.

8. In a temperature control system for an aircraft having a compressor for maintaining desired air pressures in said aircraft at varying altitudes, which compressor incidentally heats the air delivered to the aircraft, in combination, an auxiliary source of heat for said aircraft, which source of heat has a minimum temperature changing effect of substantial proportions, means for determining the effect of said hot compressed air upon said aircraft, temperature responsive means for controlling said effect determining means to graduatingly increase the effect of said hot compressed air, then place said auxiliary source of heat into `operation at a minimum and thereafter to increase its temperature changing effect upon continuous temperature change at said temperature responsive means, and other means placed in control of said effect determining means as an incident to placing said auxiliary source of heat into operation for reducing the effect of said hot compressed air.

9. In a condition controlling system, means for translating a condition changing medium,

23 rstV means for changing a condition of said medium, second means for changing a condition of said medium, means for controlling both said iirst and said second condition changing means in sequence until operation ofsaid second condition changing means is required, and means for initially reducing but not stoppingthe condition changing abilitar of said rst condition changing means when said second condition changing means is made operable.

10. In a condition controlling system, means for translating a condition changing medium, iirst means for changing a condition of said medium, second means for changing said condition of said medium, means for proportionally controlling said rst condition changing means, means for proportionally controlling said second condition changing means, means for preventing operation of said second condition changing means until a predetermined portion of its capacity is required, rst means responsive to a condition indicative of a need for operation of the present system, second means responsive to a different value of the same condition, means including said rst condition responsive means for sequentially controlling Ysaid rst and second condition changing means until said second condition changing means is placed inoperation, and means including said second condition responsive means for controlling said first condition changing means when said second condition changing means is operative.

11. In a control system for a space, compressor means for supplying air to said space, said com--v pressor means being capable of heating the said air, conduit means connecting said compressor means and said space, said conduit means including a iirst device for cooling said air and a second device for heating said air, iirst temperature responsive means adjusted to a predetermined control point, second temperature responsive means adjusted to a different control point, means including said rst temperature responsive means for controlling said cooling means and said heating means, and means including said second temperature responsive means for controlling said `cooling means when said heating means is operating.

12. In a structure having an enclosed` space, compressor means for supplying air to said space. said means being capable of heating said air, conduit means connecting said compressor means asoma? 1 I l with said space, said conduit means including a irst device for cooling said air and a second device for heating said air, means responsive to the temperature of the air discharged into said space, means responsive to the temperature of said space, means responsive to the temperature of the air being supplied to said space after it-has passed through said first device but before it passes through the second device, means including the means responsive to discharge air temperature and the means responsive to the space temperature for controlling said ilrst device, and means including the means responsive to the temperature of the air after passing through the said first device but before it passes through the said second device and the space temperature responsive means for controlling the said second device.

13.V In a condition controllingsystem for flrst and second condition changers for changing a desired condition in which the second of said condition changers must initially be placed in operation at an appreciable portion of its capacity but which may thereafter be modulated to its full capacity; in combination, means responsive to the desired condition; means for controlling each of said condition changers; switching means; and means connecting said condition responsive means, said switching means and said controlling means in such manner that upon a continuous change in demand in ne direction the first condition changer will be operated up to its full capacity and then the second condition changer will be placed in operation and the capacity of said iirst condition changer reduced as a function of said switching means.

HUBERT T. SPARROW.

REFERENCES CITED The following references are of record the ille of this patent:

UNITED STATES PATENTS Cunningham June 11, 1946 

